FIG. 1 shows a propulsion assembly 10 of the prior art, which is fastened under a wing 12 of an aircraft. The propulsion assembly 10 incorporates a turbofan 16 and a mounting pylon 14, by means of which the turbofan 16 is fastened under the wing 12. The mounting pylon 14 generally incorporates a rigid structure 18, also called primary structure, supporting first fastening components intended for mounting the turbofan 16.
These first fastening components are formed from two engine attachments 20 and 22, together with a device 24 for absorbing the thrust forces generated by the turbofan 16.
The mounting pylon 14 further incorporates second fastening components (not illustrated) enabling the mounting pylon 14 to be fastened to the wing 12. Of course, the propulsion assembly 10 is intended to be surrounded by a nacelle (not illustrated).
The mounting pylon 14 also has a plurality of secondary structures 26 added onto the rigid structure 18 and ensuring the segregation and retaining of the systems, at the same time supporting aerodynamic fairing components.
The turbofan 16 incorporates, forward, a fan casing 28 surrounding an annular fan channel, and towards aft, a central casing 30 of a smaller dimension, enclosing the core of the turbofan 16. The casings 28 and 30 are, of course, integral one with the other.
The first fastening components incorporate a forward engine attachment 20, interposed between a forward extremity of the rigid structure 18 and an upper part of the fan casing 28. Furthermore, the first fastening components incorporate the aft engine attachment 22 interposed between the rigid structure 18 and an aft part of the central casing 30.
Finally, these first fastening components incorporate the device for absorbing the thrust forces generated by the turbofan 16, this device including two links 24 (only one of which is visible on FIG. 1) placed either side of a median vertical plane P of the turbofan 16, and hinged, on one hand, on the fan casing 28, and on the other, on a safety element fastened to the rigid structure 18. The device for absorbing the thrust forces formed by the two links 24 and the safety element is designed to absorb the entirety or the majority of the forces oriented along the longitudinal direction of the turbofan 16.
The first fastening components preferably form an isostatic system of connections between the rigid structure 18 and the turbofan 16.
The forward engine attachment 20 enables the absorption of a portion of the forces oriented along the directions Y and Z, this generating high bending moments My and Mz in the forward part of the rigid structure 18, together with a torsional moment Mx. Such loads necessitate the installation of a special rigid structure 18, which takes the shape of a closed box extending from aft towards forward, substantially along the longitudinal direction X, and provided with transverse ribs (not illustrated), each taking the shape of a rectangle oriented in a transverse plane.
Such a structure is therefore relatively complex to design and to embody.